Direct electrical current is often used to separate particles and liquids by taking advantage of the electroosmotic and electrophoretic effects produced thereby. The present invention is an improvement over U.S. Pat. No. 4,561,953 to Muralidhara et al, commonly owned by the assignee of the present patent, which is incorporated by reference as if fully rewritten herein.
Additional art beyond that cited in the Muralidhara et al patent includes a patent to Thomas 2,740,756 that teaches the use of radio frequencies above 15,000 cps to induce unidirectional pulses of current in material to be dried in order to move liquid out of the material electrically even with poor electrode contact or no contact at all. The energy savings and other advantages of the present invention are realized at significantly lower frequencies and with simpler equipment. Several U.S. patents to Candor teach the use of electrostatic fields to dewater various materials as for example U.S. Pat. Nos. 4,551,924; 4,236,317; 4,189,845; 4,135,307; 4,050,162; 3,931,682; and 3,641,680 among others. Of the above, the latter two patents combine vibrational energy with an electrostatic effect to remove moisture from materials. An additional patent to Roundsley U.S. Pat. No. 4,359,826 issued Nov. 23, 1982 provides a good discussion of the electrostatic art and is incorporated herein by reference.
The present invention differs from the electrostatic art in that it is important and indeed necessary that an electrical field have associated therewith an electrical current that permeates the mass of the material to be dewatered. In addition, the high voltages that are required in electrostatic drying, in the order of several thousand volts are not needed. See for example an article by Robert R. Roundsley, Drying in the Presence of an Electrostatic Field, Tappi Journal, Vol. 68, No. 6, June 1985 (Graph page 5).